Violating Agreements
Many years ago my partner and I had a string of very good results in a Swiss match against two well regarded players. On the last hand LHO was the dealer and decided to pass holding a balanced 16 count hoping to catch us getting frisky. My partner passed with a random 8 count, and RHO with a balanced Yarborough decided to psych 1NT. With my strong NT, I passed, and now LHO had a problem, he couldn't invite with 4NT, partner would never believe him, so he just jumped to 6NT. I doubled and when the dust settled they were down 9. The point of this story is that each of the partners violated their agreements, but that neither partner had violated the laws of bridge since neither partner had any idea what the other was doing.
You may make almost any bid you like (other than psyching a strong artificial forcing opening bid) without violating the laws of bridge. The problem occurs if partner either because of discussion or experience has information about the possibilities opponents don't have. Some partnerships open “better minor” when holding 3-3 in the minors, and some of those partnerships may regularly open the weaker minor to inhibit the lead. Another example would be opening an off shape NT. If things like this happen more than once, the opponents are entitled to know about it.